The field of the invention relates generally to steam turbines, and more particularly to a rotor assembly for use with a steam turbine.
At least some known rotors are fabricated as a single forging that includes rotor coupling ends, bearing regions, packing regions, and a steampath section. Generally, the material used in fabricating such rotors is dictated by operational requirements and specifications in the higher temperature and higher pressure regions of the rotor. In at least some known rotors, a high performance steel, such as 12Cr steel, is used as a material in the high temperature and high pressure regions, as this type of material has an appropriate strength and creep capability for such operating conditions. However, manufacturing an entire rotor from such a steel material may be expensive and impractical.
At least some other known rotors are fabricated from multiple forgings that may include individually and separately manufactured rotor coupling ends, bearing regions, packing regions, and/or steampath sections. Multiple forgings enable different, more suitable and/or cost-effective materials to be used in each section of the rotor. Specifically, in steam turbine rotors in which individual components of the rotor are mechanically coupled together, materials for the rotors are generally selected based on anticipated steam conditions in the high pressure and low pressure regions. Lower grade steel, such as CrMoV steel, may be used to fabricate turbine rotor components located in the areas of lower temperatures and/or pressures. The components are then coupled together for operation. In some known rotors, the components are coupled together via a welding process.